Hello, I'm in the USA and have my Win7 Ultimate x64 system set to 24-hour time, but the current Daily thunderbird-53.0a1.en-US.win64.installer.exe installs a version with 12-hour a.m./p.m. times for the e-mails. I restart the system daily and there's no change. After I install each new Daily version with same results, I then install a copy of the version from January 7 and I'm immediately back to 24-hour time. I noticed this happened about 2 weeks ago as well, one of the Saturday versions did same but the later versions up to January 7 all were 24-hour time. This also happened without any Win7 updates happening. I had tried the Super Date Format extension which restores the 24-hour time but loses the "short date/time" format when the e-mail is received on the same day as today (ie., 24-hour time only without any date), but I'd rather just run without it. This has worked very well for a few years now until very recently. Any help would be appreciated. Thanks in advance! Greg